Prostheses are known, which are applied in parts of the human or animal body, normally made essentially by a metal support or shell to which an insert made of plastic material is coupled solidly, which facilitates the sliding of the mobile part of the prosthesis, thus allowing it to move and reducing wear on the parts.
The choice of material for the metal support and the plastic material of the insert is dictated by the use of bio-compatible materials; generally the metal support is made of pure titanium, titanium alloys, tantalum alloys, cobalt alloys, whereas the plastic material is for example high molecular weight polyethylene, polycarbonate urethane, polyether ether ketone or similar materials.
It is known to make at least the external surface of the metal support with a porous structure, the function of which is to allow the bone to bind after an implant operation, thus promoting the process of progressive osteo-integration of the prosthetic element.
The porous structure, if it is also present on the internal surface, or part of it, not only allows the osteo-integration process but can also be used to facilitate the solidarization of a wear insert made of plastic material.
One of the methods used to make the porous structure is DMSLS (Direct Metal Selective Laser Sintering). This method allows to make products and components of metal material with a solidification process of successive layers, with a predefined thickness, of powders of metal material, using laser beams. Another technique is EBM (Electron Beam Melting), which allows to make components, for example of titanium, starting from a bath of titanium powders, by means of a melting process in conditions of high vacuum, and solidification of successive layers as in the DMSLS technique.
In known solutions, the insert is normally made in advance already in the form it will have to have once made solid with the prosthetic element, and then attached to it during the course of the implant operation, or already prepared in advance.
In order to allow the plastic insert to be made solid with the metal support, a known solution provides that the plastic insert, already pre-formed, is heated until a pre-established level of softness is reached, and subsequently the two parts, plastic and metal, are made solid with each other by pressing, in this way making one part of the surface of the plastic material penetrate, in a controlled manner, into the pores of the metal element.
One disadvantage of this solution is that it is necessary to control carefully the level of heating and of penetration of the plastic insert into the metal support, because the pores must not be completely filled since these are required for the process of osteo-integration after the implant.
Another disadvantage of this type of prosthetic element is that it is necessary to make the plastic insert in advance in the desired form, which entails additional operations, and also reduces the possibility of keeping in store a series of inserts of a suitable shape and size.
U.S. Pat. No. B1-6,682,567 describes a prosthetic component having an external surface suitable for osteo-integration and an internal polymer lining. The prosthetic component, in the solution described, is obtained in ceramic material, starting from a green body that is lined on the inner side and the outer side by a porous layer, and then sintered in the furnace.
On the inside of the ceramic body the internal polymer lining is then injected. Incidentally, U.S. '567 hypothesizes using any metal substance to make the shell, for example titanium. The method to make the porous titanium shell is not described.
US 2009/0084491 A1 describes another solution in which a porous layer is applied, for example glued or welded, on a metal base, and then the polymer layer is attached on the porous layer.
One purpose of the present invention is to make a prosthetic element of the type indicated above, that is easier to make, avoiding complex preparation operations and limiting the times and costs of production.
Another purpose of the present invention is to avoid operations of pre-forming the plastic insert before it is made solid with the support structure, and to avoid having to manage stocks in store.
Another purpose of the present invention is to achieve a more stable and resistant union of the metal material and the plastic material.
Another purpose of the present invention is to allow to make integrated prosthetic elements with a more limited thickness compared with state-of-the-art integrated prosthetic elements.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.